On the atmospheric corrosion of metals which are covered with thin electrolyte layers-iii. the measurement of polarisation curves on metal surfaces which are covered by thin electrolyte layers

Abstract In this study for the first time a circuit is presented which allows the measurement of polarisation curves on metal surfaces which are covered by electrolyte layers as thin as 2 μm. The circuit does not need any Luggin capillary but uses a Kelvin probe as a reference electrode which does not touch the surface under investigation. Results are discussed which have been obtained with platinum and iron as working electrodes. On iron electrodes, during drying the rate of the oxygen reduction is accelerated due to a faster transport of oxygen through the thin electrolyte layer. The surface is passivated either due to the precipitation of corrosion products or due to pH-changes inside the thin electrolyte layer. This confirms the model of the atmospheric corrosion of iron and steel presented in part 2 of this paper.